Mozilla snuffs password pilfering Firefox add-on

Beware unreviewed software calling itself Mozilla Sniffer

Mozilla has disabled and block-listed a Firefox add-on containing code that nabs login data sent to any website and reroutes it to a remote server.

The add-on — known as, um, Mozilla Sniffer — was uploaded to the Firefox add-on site on June 6, and the malicious code was discovered on Monday, after which the add-on was block-listed. This means netizens who installed the add-on will be prompted to remove it. Mozilla also says that, yes, anyone who has installed the add-on should change their web passwords tout de suite.

"If a user installs this add-on and submits a login form with a password field, all form data will be submitted to a remote location," Mozilla said in a Tuesday blog post, before adding that the remote server charged with collecting passwords appeared to be down.

According to Mozilla, the Sniffer was downloaded about 1,800 times, and as of Tuesday, there were 334 active users.

The add-on had not been reviewed by Mozilla. It was marked as "experimental", meaning that anyone who attempted to install it received a warning that the code had not been reviewed. Such unreviewed add-ons are merely scanned for viruses, trojans, and other malware.

Mozilla, however, is (slowly) developing a new security model designed to prevent unreviewed add-ons from being served to world+dog. "Having unreviewed add-ons exposed to the public, even with low visibility, has been previously identified as an attack vector for hackers. For this reason, we’re already working on implementing a new security model for addons.mozilla.org that will require all add-ons to be code-reviewed before they are discoverable in the site."

Mozilla also said it had discovered a security vulnerability in version 3.0.1 of a far more popular add-on known as CoolPreviews, which displays previews of webpages when you mouse over links. Version 3.0.1 and earlier versions have been disabled, and a patched add-on has been uploaded to addons.mozilla.org.

According to Mozilla, when the user mouses over a link, the add-on could execute remote JavaScript code with local chrome privileges, giving an attacker control over the user's machine. "If a user has a vulnerable version installed and clicks on a malicious link that targets the add-on, the code in the malicious link will run with local privileges, potentially gaining access to the file system and allowing code download and execution," Mozilla said.

About 177,000 users had a vulnerable version of the add-on installed as of Tuesday — less than 25 per cent of total users. Mozilla intends to block-list vulnerable versions "very soon." ®